It is very different on mobile. I just took some screenshots of Google search on Firefox on Android before and after enabling an addon that sets my user agent to Chrome on Google sites: https://imgur.com/a/P9zDn7B
You can sometimes trigger similar changes in appearance to the search results view by switching to incognito or clearing your cookies - Google often A/B tests or performs slow rollouts of changes like this, a difference in appearance could just be because a new user agent string got you placed into a different release group.
Honestly at this point I’d like to give up on the user agent header and have everybody say they’re Chrome all the time.
Incidentally, this is far from the first time google has been caught heavily optimizing exclusively for their own browsers, which, to be clear, is quite probably not explicit policy - but is monopolistic abuse nonetheless. Remember the youtube polymer redesign? The Edge HW acceleration-breaking invisible layers? I get the feeling they just don't test in other browsers nearly as well.
Given google's history here you really shouldn't be giving them the benefit of the doubt in this matter; at best they're consistently, repeatedly negligent; but it's at least conceivable there's culture of giving additional other google teams; which is a form of monopolistic power abuse.
Not a fan of Firefox and I refuse to like or use chrome.
Yawn.